First-in-Human Phase I Trial Combining Biologically Guided Radioimmunotherapy (RIT) Using a 90Y-Anti-CD25 Monoclonal Antibody (Mab) with CT-guided Total Marrow and Lymphoid Irradiation (TMLI) in Relapsed and Refractory (R/R) Acute Leukemia

PURPOSE/OBJECTIVE(S)

Patients with R/R acute leukemia after allogeneic hematopoietic cell transplant (alloHCT) have a dismal prognosis with 3-year survival rates of < 20%. To improve outcomes, innovative targeted forms of organ sparing radiotherapy, such as tumor-specific RIT and TMLI, are needed to dose escalate with acceptable toxicities, especially in patients ≥ age 60 years who cannot tolerate total body irradiation (TBI) / myeloablative regimens and who have a poor prognosis. CD25 is an ideal RIT target given its expression in acute leukemias, association with poor prognosis, and expression by leukemia stem cells. In this phase I trial (NCT05139004) we hypothesized that combining dose escalated 90Y-anti-CD25 RIT with fixed dose TMLI 12 Gy, fludarabine (flu), and melphalan (mel) in patients with R/R disease is safe and associated with acceptable toxicities.

MATERIALS/METHODS

The primary objective of this trial is to determine the maximum tolerated dose and recommended phase 2 dose of 90Y-anti-CD25 Mab (Day -15) with 12 Gy TMLI (1.5 Gy twice a day, days -8 to -5), flu (30 mg/m2/d days -5 to -2), and mel (100 mg/m2, day -2) in patients ≥ 60 years old or with a HCT-comorbidity index ≥ 2 and with R/R AML, ALL or myelodysplastic syndrome (MDS) scheduled to undergo alloHCT from a matched donor. TMLI mean organ dose constraints for kidney, lung and liver were 4 Gy. Planned dose levels of 90Y-anti-CD25 were 0.3, 0.4, and 0.5 mCi/kg. 111In-anti-CD25 (5 mCi) was co-infused followed by serial nuclear scans to assess dosimetry and biodistribution.

RESULTS

To date 5 patients (ages 31-74) with R/R AML have been treated. Marrow and circulating blasts ranged from 10-36% and 9-44%, respectively. For the 3 patients at 0.3 mCi/kg, follow-up ranged from 89-191+ days. 90Y/111In-anti-CD25 nuclear scans demonstrated persistent uptake in bone out to 144 hours, which was associated with a decline in circulating blasts. After combined RIT and TMLI, mean doses (Gy) to lungs ranged from 5.7-6.5, to kidneys from 7.5-8.2 and to liver from 7.2-11.6. No dose-limiting toxicities (DLT) were observed. All 3 patients achieved CR on day +30 bone marrow biopsies and 2 remained in CR on day +90 biopsies. Two patients have recently been treated at the 0.4 mCi/kg dose level. The results of patients treated at the higher dose levels will be provided.

CONCLUSION

Dose escalation by adding 90Y-anti-CD25 RIT at 0.3 mCi/kg to 12 Gy TMLI was safe, including in older patients, with no dose-limiting toxicities, mean critical organ doses lower than conventional myeloablative TBI, and encouraging response rates. The toxicity profile and dose estimates at 0.3 mCi/kg predict that the planned higher dose levels will also be feasible with acceptable toxicities. RIT and TMLI are complementary and when combined address the limitations of each modality. Combining these targeted therapies may be a superior strategy to intensify dose to leukemia compared to dose escalation of either modality alone.

Abstract PD4-12: Use of 64Cu-DOTA-trastuzumab positron emission tomography (PET) to predict response to ado-trastuzumab emtansine (TDM1)

Background: We have demonstrated that 64Cu-DOTA trastuzumab is an effective PET imaging agent for HER2 positive breast cancer and are now seeking to evaluate the methodology for prediction of response and benefit to ado-trastuzumab emtansine (TDM1) in women with metastatic disease.

Methods: Patients with metastatic breast cancer were eligible if they had biopsy confirmed HER2 + disease, at least 1 site of metastasis 2.0 cm or larger outside the biopsy site, and were to receive TDM1 as therapy. Pretreatment staging included 18F-FDG/PET. Prior to injection of 64Cu-DOTA-trastuzumab, patients received 45 mg of cold trastuzumab to reduce liver uptake. PET-CT scans were obtained at 21-25 h and 47-48 h over fields of view chosen in reference to 18F-FDG scans. TDM1 was administered at a dose of 3.6 mg/kg every 3 weeks. Restaging 18F-FDG/PET was performed every 2 cycles, and response to therapy was determined by PERCIST criteria. The radiolabel uptake was measured in terms of maximum voxel standardized uptake value (SUVmax).

Results: Ten women enrolled on study and are evaluable for response; three continue on TDM1 for 22-40 months and four patients remained on treatment for at least 1 year. The median age was 54.5 years (48-83 years); seven received prior trastuzumab-containing chemotherapy 3 wks to 55 months prior to study entry. HER2 was positive by IHC in 5 and by FISH in 5 (3 were 2+ by IHC; 1 was 1+ and 1 indeterminate). Complete or partial metabolic response was observed in 5 patients. Patients had their average SUVmax on 64Cu-DOTA trastuzumab PET (aSUVmax) assessed in addition to individual assessments on up to 8 lesions on both Day1 and Day2. The mean aSUVmax was (6.3, 8.8) for responding patients and (4.4, 5.2) for non-responder (day1, day2). The difference between responders and non-responders on Day1 aSUVmax was marginally significant (p=0.06), but significant on Day2 (p=0.04). The three highest aSUVmax on both day1 and day2 were three of the four patients with PFS&gt;1 year. Data on the relationship of 64Cu-DOTA trastuzumab PET to IHC and FISH, and individual lesion SUVmax including evidence suggesting a potential threshold effect will be presented.

Conclusions: In women with biopsy confirmed HER2 positive metastatic disease, 64Cu-DOTA-trastuzumab PET imaging is predictive for response to TDM1.

Citation Format: Mortimer JE, Bading JR, Frankel P, Tumyan L, Tran TT, Rockne RC, Shively JE, Gidwaney N, Park J, Colcher DM. Use of 64Cu-DOTA-trastuzumab positron emission tomography (PET) to predict response to ado-trastuzumab emtansine (TDM1) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD4-12.

CAMK2γ in intestinal epithelial cells modulates colitis-associated colorectal carcinogenesis via enhancing STAT3 activation

Inflammation is one of the major risk factors for cancer. Here, we show that calcium/calmodulin-dependent protein kinase II gamma (CAMK2γ) in intestinal epithelial cells (IECs) modulates inflammatory signals and promotes colitis-associated cancer (CAC) in mice. We have identified CAMK2γ as a downstream target of colitis-induced WNT5a signaling. Furthermore, we have shown that CAMK2γ protects against intestine tissue injury by increasing IEC survival and proliferation. CAMK2γ knockout mice displayed reduced CAC. Furthermore, we used bone marrow transplantation to reveal that CAMK2γ in IECs, but not immune cells, was crucial for its effect on CAC. Consistently, transgenic over-expression of CAMK2γ in IECs accelerated CAC development. Mechanistically, CAMK2γ in IECs enhanced epithelial STAT3 activation to promote survival and proliferation of colonic epithelial cells during CAC development. These results thus identify a new molecular mechanism mediated by CAMK2γ in IECs during CAC development, thereby providing a potential new therapeutic target for CAC.

Primary structure and neuronal effects of alpha-bag cell peptide, a second candidate neurotransmitter encoded by a single gene in bag cell neurons of Aplysia

A discharge of impulse activity in a group of neuroendocrine cells, the bag cells, produces several types of prolonged responses in various identified neurons of the abdominal ganglion of Aplysia. Two excitatory responses are almost certainly mediated by egg-laying hormone, but this peptide cannot account for other responses, such as inhibition of left upper quadrant neurons. We report here the isolation from bag cell clusters of three structurally similar peptides, seven, eight, and nine residues long, that are candidate transmitters for mediating bag cell-induced inhibition. They may also serve as autoexcitatory transmitters since the seven-residue peptide produces a slow depolarization of the bag cells similar to that which occurs during bag cell discharge. The amino acid sequence of the largest peptide, termed alpha-bag cell peptide[1-9], is H-Ala-Pro-Arg-Leu-Arg-Phe-Tyr-Ser-Leu-OH. The other two peptides are identical to alpha-BCP[1-9] except that they lack the COOH-terminal Ser-Leu or leucine residues. The three peptides inhibit left upper quadrant neurons at relative potencies of 10:30:1 (seven-, eight-, and nine-residue peptides, respectively). Recent molecular genetic analysis shows that both alpha-BCP[1-9] and egg-laying hormone are encoded by the same bag cell-specific gene. The multiple neuronal effects of bag cells are therefore likely to be mediated by at least two transmitters that are cleaved from a common precursor molecule.

Role of CEACAM1 isoforms in an in vivo model of mammary morphogenesis: mutational analysis of the cytoplasmic domain of CEACAM1-4S reveals key residues involved in lumen formation

CEACAM1 (carcinoembryonic antigen-related cell adhesion molecule 1) is a type I transmembrane glycoprotein expressed in epithelial cells with three or four extracellular domains (ECDs) and either long or short cytoplasmic domain isoforms. We have previously shown that the four extracellular domains, short cytoplasmic domain isoform, CEACAM1-4S, plays an essential role in lumen formation in an in vitro model of mammary morphogenesis. In this study, we transfected MCF-7 cells with either the long or short cytoplasmic domain isoforms of CEACAM1, and grew the cells in humanized mammary mouse fat pads in NOD/SCID mice. In this in vivo model, only the long cytoplasmic domain isoform, CEACAM1-4L, formed glands with lumen. On the basis of other studies that revealed phosphorylation of key Thr and Ser residues in the short cytoplasmic domain, we introduced phosphorylation mimic (for example, Thr or Ser to Asp) or null (Thr or Ser to Ala) mutations into the cytoplasmic domain of CEACAM1-4S and tested them in the in vivo model. Mutation of either Thr or Ser to Asp or the double mutant Thr+Ser to Asp, but not the null mutants, induced gland formation with a central lumen-containing apoptotic cells. Moreover, the phosphorylation mimic mutants of CEACAM1-4S induced downregulation of beta1-integrin, overexpression of beta2-integrin, inhibited phosphorylation of focal adhesion kinase (pTyr-397) and resulted in myofibroblast differentiation as characterized by expression of vimentin, alpha-smooth muscle actin and beta2-integrin, as well as the production of abundant extracellular matrix.

Protein epitopes in carcinoembryonic antigen. Report of the ISOBM TD8 workshop

To characterize antigenic sites in carcinoembryonic antigen (CEA) further and to investigate whether there are differences between colon tumor CEA and meconium CEA (NCA-2) that can be detected by anti-CEA monoclonal antibodies (MAb), 19 new anti-CEA MAb were analyzed with respect to specificity, epitope reactivity and affinity. Their reactivities were compared with 10 anti-CEA MAb with known CEA-domain binding specificity that have previously been classified into five nonoverlapping epitope groups, GOLD 1-5. Cross-inhibition assays with antigen-coated microtiter plates and immunoradiometric assays were performed in almost all combinations of MAbs, using conventionally purified CEA (domain structure: N-A1B1-A2B2-A3B3-C) from liver metastasis of colorectal carcinomas, recombinant CEA, meconium CEA (NCA-2), truncated forms of CEA and NCA (CEACAM6) as the antigens. The affinity of the MAbs for CEA was also determined. The new MAbs were generally of high affinity and suitable for immunoassays. Three new MAbs were assigned to GOLD epitope group 5 (N-domain binding), 3 MAbs to group 4 (A1B1 domain), 1 to group 3 (A3B3 domain), 3 to group 2 (A2B2 domain) and 3 to group 1 (also the A3B3 domain). Three MAbs formed a separate group related to group 4, they were classified as GOLD 4' (A1B1 domain binding). The remaining 3 MAbs appear to represent new subspecificities with some relationship to GOLD groups 1, 2 or 4, respectively. Five MAbs, all belonging to epitope group 1 and 3, reacted strongly with tumor CEA but only weakly or not at all with meconium CEA, demonstrating that the two products of the CEA gene differ from each other, probably due to different posttranslational modifications.

Carcinoembryonic antigen cell adhesion molecule 1 directly associates with cytoskeleton proteins actin and tropomyosin

CEA cell adhesion molecule 1 (CEACAM1), a type 1 transmembrane and homotypic cell adhesion protein belonging to the carcinoembryonic antigen (CEA) gene family and expressed on epithelial cells, is alternatively spliced to produce four major isoforms with three or four Ig-like ectodomains and either long (CEACAM1-L) or short (CEACAM1-S) cytoplasmic domains. When murine MC38 (methylcholanthrene-induced adenocarcinoma 38) cells were transfected with human CEACAM1-L and stimulated with sodium pervanadate, actin was found to co-localize with CEACAM1-L at cell-cell boundaries but not in untreated cells. When CEACAM1-L was immunoprecipitated from pervanadate-treated MC38/CEACAM1-L cells and the associated proteins were analyzed by two-dimensional gel analysis and mass spectrometry, actin and tropomyosin, among other proteins, were identified. Whereas a glutathione S-transferase (GST) fusion protein containing the l-isoform (GST-Cyto-L) bound poorly to F-actin in a co-sedimentation assay, the S-isoform fusion protein (GST-Cyto-S) co-sedimented with F-actin, especially when incubated with G-actin during polymerization (K(D) = 7.0 microm). Both GST-Cyto-S and GST-Cyto-L fusion proteins bind G-actin and tropomyosin by surface plasmon resonance studies with binding constants of 0.7 x 10(-8) and 1.0 x 10(-7) m for GST-Cyto-L to G-actin and tropomyosin, respectively, and 3.1 x 10(-8) and 1.3 x 10(-7) m for GST-Cyto-S to G-actin and tropomyosin, respectively. Calmodulin or EDTA inhibited binding of the GST-Cyto-L fusion protein to G-actin, whereas calmodulin and G-actin, but not EDTA, stimulated binding to tropomyosin. A biotinylated 14-amino acid peptide derived from the juxtamembrane portion of the cytoplasmic domain of CEACAM1-L associated with both G-actin and tropomyosin with K(D) values of 1.3 x 10(-5) and 1.8 x 10(-5) m, respectively. These studies demonstrate the direct interaction of CEACAM1 isoforms with G-actin and tropomyosin and the direct interaction of CEACAM1-S with F-actin.

Controlling deamidation rates in a model peptide: effects of temperature, peptide concentration, and additives

The rate of deamidation of the Asn residue in Val-Tyr-Pro-Asn-Gly-Ala (VYPNGA), a model peptide, was determined at pH 9 (400 mM Tris buffer) as a function of temperature and peptide concentration. Over the temperature range 5-65 degrees C, deamidation followed Arrhenius behavior, with an apparent activation energy of 13.3 kcal/mol. Furthermore, increasing the peptide concentration slows the rate of deamidation. Self-stabilization with respect to deamidation has not been reported previously. The rate of deamidation was also determined in the presence of sucrose and poloxamer 407 (Pluronic F127). In both cases, the rate of deamidation was retarded by up to 40% at 35 degrees C. In aqueous solutions containing poloxamer 407, the degree of stabilization is independent of formation of a reversible thermosetting gel. With sucrose, maximum reduction in the deamidation rate was attained with as little as 5% (w/v). Addition of sucrose results in a greater conformational preference for a type II beta-turn structure, which presumably is less prone to intramolecular cyclization and subsequent deamidation.

Chelators for radioimmunotherapy: I. NMR and ab initio calculation studies on 1,4,7,10-tetra(carboxyethyl)-1,4,7,10-tetraazacyclododecane (DO4Pr) and 1,4,7-tris(carboxymethyl)-10-(carboxyethyl)-1,4,7,10-tetraazacyclododecane (DO3A1Pr)

This work describes the modification of the chelating agent 1,4,7,10-tetraazacyclododecane-N,N',N' ',N' "-tetraacetic acid (DOTA) to improve the rate of metal loading for radioimmunotherapy applications. Previous ab initio calculations predicted that the compounds 1,4,7,10-tetra(carboxyethyl)-1,4,7,10-tetraazacyclododecane (DO4Pr) and 1,4,7-tris(carboxymethyl)-10-(carboxyethyl)-1,4,7,10-tetraazacyclododecane (DO3A1Pr) have a ca. 2000-fold improvement in yttrium metal loading rates compared to those of DOTA (Jang, Y. H.; Blanco, M.; Dasgupta, S.; Keire, D. A.; Shively, J. E.; Goddard, W. A., III. J. Am. Chem. Soc. 1999, 121, 6142-6151). In this study, we report the synthesis, purification, (1)H-NMR chemical shift assignments, pK(a) values, metal loading rate measurements, and additional ab initio calculations of these two compounds. The yttrium loading rates of DO3A1Pr are approximately twice those of DOTA, at pH 4.6 and 37 degrees C. The NMR data indicates that the DO4Pr analogue forms a stable type I complex but does not form a type II complex. The new ab initio calculations performed on DO4Pr and DO3A1Pr indicate that the rate-determining step is the deprotonation of the first macrocycle amine proton, not the second proton as assumed in the previous calculations. The new calculations predict an improvement in the rate of metal loading that more closely matches the experimentally observed change in the rate.

Mammalian expression and hollow fiber bioreactor production of recombinant anti-CEA diabody and minibody for clinical applications

Genetically engineered radiolabeled antibody fragments have shown great promise for the radioimmunoscintigraphy of cancer. Retaining the exquisite specificity of monoclonal antibodies yet smaller in molecular size, antibody fragments display rapid tumor targeting and blood clearance, a more uniform distribution in the tumor, and present a lower potential to elicit an immune response. However, one of the factors that has limited clinical evaluation of these antibody-derived proteins has been the difficulty in expressing and purifying the quantities necessary for clinical trials. This study outlines the capability of mammalian expression for the production of recombinant antibody fragments intended for clinical use. Two anti-carcinoembryonic antigen antibody fragments, the T84.66/212 Flex minibody (scFv-C(H)3) and the T84.66 diabody (scFv dimer) have been previously expressed and have shown excellent radioimaging properties in tumor bearing animals. To proceed toward human studies, these high affinity recombinant fragments and a second minibody version, the T84.66/GS18 Flex minibody, were expressed using a high-level mammalian expression system. Production of all three antibody fragments in a small-scale hollow fiber bioreactor resulted in 137-307 mg of crude antibody harvest. A purification protocol that employed ceramic hydroxyapatite and anion exchange chromatography resulted in 50-150 mg of purified T84.66 diabody and T84.66 minibody. The development of this level of research grade material established conditions for clinical production as well as provided material to complete pre-clinical studies and undertake protein crystallization studies. Scale-up for clinical studies produced 3.4 g of the T84.66 minibody in the harvest. A portion of this material was purified yielding 180 mg of highly purified T84.66 minibody intended for pilot radioimmunoscintigraphy studies of carcinoembryonic antigen (CEA) positive disease.

Fusion proteins of B7.1 and a carcinoembryonic antigen (CEA)-specific antibody fragment opsonize CEA-expressing tumor cells and coactivate T-cell immunity

Genetic engineering can be used to generate antigen-specific molecules for improved tumor immunotherapy. We have constructed genes coding for fusion proteins consisting of a high-affinity antibody single-chain antibody fragment (scFv) specific for the human carcinoembryonic antigen (CEA) and the costimulation domain of the murine B7.1 molecule (mB7.1) linked to the antibody moiety by an IgG3 peptide linker. The hybrid genes were constructed in 2 orientations, one with the scFv located N-terminal to mB7.1 and one vice versa. Soluble proteins were expressed by CHO cells, purified using anti-idiotype-affinity chromatography and characterized by tumor-cell binding and costimulation activity. When tumor cells expressing CEA on the cell membrane were opsonized with the CEA-specific costimulators, both fusion proteins specifically stimulated murine T-cell preparations to proliferate in a similar manner. Our data suggest that "costimulation coating" of tumor cells may be a suitable approach for activation of a sustained cellular antitumor response. It also provides the opportunity to increase tumor immunogenicity using easily generated soluble fusion proteins that advantageously link biological functions of both the humoral and the cellular arm of the specific immune system.

Fusion proteins of B7.1 and a carcinoembryonic antigen (CEA)-specific antibody fragment opsonize CEA-expressing tumor cells and coactivate T-cell immunity

Genetic engineering can be used to generate antigen-specific molecules for improved tumor immunotherapy. We have constructed genes coding for fusion proteins consisting of a high-affinity antibody single-chain antibody fragment (scFv) specific for the human carcinoembryonic antigen (CEA) and the costimulation domain of the murine B7.1 molecule (mB7.1) linked to the antibody moiety by an IgG3 peptide linker. The hybrid genes were constructed in 2 orientations, one with the scFv located N-terminal to mB7.1 and one vice versa. Soluble proteins were expressed by CHO cells, purified using anti-idiotype-affinity chromatography and characterized by tumor-cell binding and costimulation activity. When tumor cells expressing CEA on the cell membrane were opsonized with the CEA-specific costimulators, both fusion proteins specifically stimulated murine T-cell preparations to proliferate in a similar manner. Our data suggest that "costimulation coating" of tumor cells may be a suitable approach for activation of a sustained cellular antitumor response. It also provides the opportunity to increase tumor immunogenicity using easily generated soluble fusion proteins that advantageously link biological functions of both the humoral and the cellular arm of the specific immune system.

Accumulation of radiolabeled anti-CEA antibody (mT84.66) in the case of multiple LS174T tumors in a nude mouse model

A comparison was made between labeled antibody accumulations in nude mice having either single or multiple human xenografts. The LS174T tumors were implanted subcutaneously. All animals were given 2 micrograms of labeled murine anti-carcinoembryonic antigen (CEA) monoclonal antibody 111In-mT84.66. Some animals were also given specific antibody pretreatment (SAP) of 200 micrograms of unlabeled mT84.66 to reduce liver accumulation of activity. In order to represent these multiple tumor examples, a simple initial-phase pharmacokinetic model was first fitted to each of the two groups (SAP and PBS treated) of single-tumor animals. Using the resultant six non-adjustable parameters as constants, the n = 1 uptake model was then used to represent tumor, liver and blood accumulations (%injected dose/organ) in the multiple-tumor animals. The model was found to be a good representation; in particular, it had far better agreement than single tumor predictions in the PBS mice. Differences between the single-tumor accumulations and those seen in multiple tumor examples were generally between two- and three-fold. The model also demonstrated that the result of SAP was to essentially eliminate the effect of liver targeting of tumor-secreted CEA. We conclude that an initial-phase one-tumor model can describe the decrease of accumulation of activity in the case of multiple tumors in nude mice in both untreated (PBS) and pretreated conditions. Implications for clinical imaging and therapy with monoclonal agents are discussed.

Tumor targeting of radiometal labeled anti-CEA recombinant T84.66 diabody and t84.66 minibody: comparison to radioiodinated fragments

Recombinant antibody fragments offer potential advantages over intact monoclonal antibodies in the radioimmunoscintigraphy (RIS) of solid tumors. Due to their smaller molecular size, antibody fragments have shown rapid tumor targeting and blood clearance, a more uniform tumor distribution and a lower potential to elicit a human immune response. Previously, we have expressed two genetically engineered antibody fragments, the T84.66 diabody (scFv dimer) and the T84.66 minibody (scFv-CH3 dimer), specific to carcinoembryonic antigen (CEA). When radioiodinated, both antibody fragments exhibited rapid tumor targeting and rapid blood clearance in xenografted mice. To extend and optimize their future clinical RIS utility with radiometals, these antibody fragments were conjugated with the macrocycle 1,4,7,10-tetraazacyclododecane N,N',N' ',N' "-tetraacetic acid (DOTA) and labeled with 111In. Tumor targeting and biodistribution studies were carried out in athymic mice xenografted with a human colorectal tumor cell line, LS174T. The [111In]T84.66 diabody (55 kDa) exhibited very rapid tumor targeting with 12.5 +/- 0.4% injected dose per gram (% ID g(-1) +/- standard error) at 2 h and reached a maximum of 13.3 +/- 0.9% ID g(-1) at 6 h. However, kidney uptake was observed to reached a peak of 183.5 +/- 21.0% ID g(-1) at 6 h, a result similar to that reported by others for other low molecular weight fragments labeled with radiometals. Preadministration of an oral dose of D-lysine resulted in a 59% lowering of the renal accumulation at 6 h, but was accompanied by a 31% reduction of tumor uptake to 9.2 +/- 1.2% ID g(-1). The second recombinant antibody fragment, the [111In]T84.66 minibody (80 kDa), displayed rapid tumor targeting of 14.2 +/- 6.1% ID g(-1) at 2 h, and reached a maximum activity of 24.5 +/- 6.1% ID g(-1) by 12 h. Renal uptake achieved a plateau of 12-13% ID g(-1) which cleared to 7.2% ID g(-1) at 72 h. However, hepatic uptake was elevated and reached a maximum of 26.0 +/- 1.0% ID g(-1) at 12 h in these xenograft-bearing mice. Experiments in nontumor bearing mice showed a reduction of hepatic activity at 12 h to 16.6 +/- 1.5% ID g(-1), indicative of an intrinsic hepatic accumulation of the [111In]DOTA-T84.66 minibody or metabolites. While the anti-CEA [111In]DOTA-T84.66 diabody and T84.66 minibody retain the rapid tumor targeting properties of the radioiodinated form, the normal organ accumulation (kidneys and liver, respectively) of the [111In]DOTA forms appeared problematic for RIS and RIT applications. Development of alternative blocking strategies or new metabolizable chelates are under investigation to enhance the utility of the radiometal form of these and other promising recombinant antibody fragments.

An improved method for conjugating monoclonal antibodies with N-hydroxysulfosuccinimidyl DOTA

A simple, water-soluble procedure for conjugation of monoclonal antibodies to 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA) has been improved by optimizing pH, buffer, and temperature conditions for the preparation of N-hydroxysulfosuccinimidyl DOTA and its conjugation to the human/murine chimeric anti-carcinoembryonic antigen antibody cT84.66. This improved method results in a 6-fold increase in conjugation efficiency, a 3-7-fold decrease in antibody cross-linking, a more homogeneous population of conjugate species, and a 5-fold decrease in the quantities of reagents needed for conjugation. The cT84.66-DOTA conjugate was labeled to high specific activity with 111In, 90Y, 88Y, 64Cu, and 67Cu, affording near-quantitative incorporation of the majority of these radiometals. This improved conjugation procedure facilitates large-scale production and radiometal labeling of cT84.66-DOTA for clinical radioimmunotherapy trials.

Metabolism and renal clearance of 111In-labeled DOTA-conjugated antibody fragments

Radiometal-labeled antibody fragments are promising reagents for radioimmunotherapy due to their high tumor uptake and rapid pharmacokinetics, but their therapeutic potentials are limited by high uptake and retention in the kidney. Identification of metabolic products is a first step in designing rationale approaches to lower kidney uptake. Previous studies in rats have shown that 111In-labeled DTPA-conjugated antibody fragments (via lysine residues) were degraded to an DTPA-epsilon-amino-lysine derivative and retained in the lysosomal compartments of the liver and kidney [Rogers et al. (1995) Cancer Res. 55, 5714s-5720s]. To determine the metabolic profile of another widely used metal-chelate, [111In]DOTA conjugated to lysines in antibody fragments via active ester chemistry, we analyzed kidney homogenates from nude mice injected with an [111In]DOTA-Fab generated enzymatically from the anti-lymphoma intact antibody Rituxan. The major kidney metabolite was identified as [111In]DOTA-epsilon-amino-lysine by comparison to an authentic synthetic standard. This end product was also identified in the urine, along with relatively small amounts of [111In]DOTA-Fab. Since injection of [111In]DOTA-epsilon-amino-lysine into nude mice resulted in rapid clearance into the urine without kidney retention, it is likely that the renal retention observed was due to kidney uptake of [111In]DOTA-Fab, followed by lysosomal degradation to [111In]DOTA-epsilon-amino-lysine, which is only slowly cleared from this compartment. This observation is supported by autoradiographs of the kidney showing rapid localization of radioactivity into the distal regions of the kidney cortex. To extend this analysis to clinical trials, we have also analyzed urine taken from a patient injected with the intact antibody [111In]DOTA-cT84.66. In that example, we found that the major radioactive species was also [111In]DOTA-epsilon-amino-lysine.

Numerical selection of optimal tumor imaging agents with application to engineered antibodies

Three analytic indicators were used to compare five members of a monoclonal antibody (Mab) family. The cognates consisted of the genetically engineered intact chimeric IgGI (cT84.66) and related engineered fragments [scFv, diabody, minibody, F(ab')2] reactive against the same epitope of carcinoembryonic antigen (CEA). All analyses were based on radioiodinated Mabs targeting to colorectal xenografts of LS174T tumors in nude mice. Affinity constants were evaluated initially. A second indicator was the imaging figure of merit (IFOM) which determines how rapidly a statistically significant tumor image can be acquired. Finally, deconvolution was used to determine tumor temporal response to an arterial bolus. This last analysis gave the possible tumor accumulation in the absence of normal tissue sequestration. Affinities were all in excess of 10(8) M-1 and were highest for the divalent Mabs. Using the IFOM criterion, an 131I label was best suited as a radiolabel for the intact (IgG) T84.66, while an 123I label indicated optimal imaging with either minibody or F(ab')2. Deconvolution analyses showed that divalent members behaved similarly while the univalent member (scFv) had a tumor residence time smaller by an order of magnitude. The diabody had the largest impulse response function, but renal uptake may limit its present usefulness.

A phase I radioimmunotherapy trial evaluating 90yttrium-labeled anti-carcinoembryonic antigen (CEA) chimeric T84.66 in patients with metastatic CEA-producing malignancies

Chimeric T84.66 (cT84.66) is a genetically engineered human/murine chimeric IgG, with high affinity and specificity to carcinoembryonic antigen (CEA). The purpose of this Phase I dose escalation therapy trial was to evaluate the toxicities, biodistribution, pharmacokinetics, tumor targeting, immunogenicity, and organ and tumor absorbed dose estimates of cT84.66 labeled with 90Y. Patients with metastatic CEA-producing malignancies were first administered 5 mCi 111In-labeled DTPA-cT84.66 (5 mg), followed by administration of the therapy dose of 90Y-labeled DTPA-cT84.66 1 week later. The therapy infusion was immediately followed by a 72-h administration of DTPA at 250 mg/m2/24 h. Dose levels of administered activity ranged from 5 to 22 mCi/m2 with three to six patients per level. Serial nuclear scans, blood samples, and 24-h urine collections were performed out to 5 days after infusion. Human antichimeric antibody response was assayed out to 6 months. Patients were administered up to 3 cycles of therapy every 6 weeks. Radiation absorbed doses to organs were estimated using a five compartment model and MIRDOSE3. Twenty-two patients received at least one cycle of therapy, with one individual receiving two cycles and two receiving three cycles of therapy. All were heavily pretreated and had progressive disease prior to entry in this trial. Reversible leukopenia and thrombocytopenia were the primary dose-limiting toxicities observed. Maximum tolerated dose was reached at 22 mCi/ m2. In general, patients with liver metastases demonstrated more rapid blood clearance of the antibody. Thirteen patients developed an immune response to the antibody. Average radiation doses to marrow, liver, and whole body were 2.6, 29, and 1.9 cGy/mCi 90Y, respectively. Dose estimates to tumor ranged from 66 to 1670 cGy (8.7 to 52.2 cGy/mCi 90Y) for each cycle of therapy delivered. Although no major responses were observed, three patients demonstrated stable disease of 12-28 weeks duration and two demonstrated a mixed response. In addition, a 41-100% reduction in tumor size was observed with five tumor lesions. 90Y-labeled cT84.66 was well tolerated, with reversible thrombocytopenia and leukopenia being dose limiting. Patients with extensive hepatic involvement by tumor demonstrated unfavorable biodistribution for therapy with rapid blood clearance and poor tumor targeting. Average tumor doses when compared with red marrow doses indicated a favorable therapeutic ratio. Stable disease and mixed responses were observed in this heavily pretreated population with progressive disease. This trial represents an important step toward further improving the therapeutic potential of this agent through refinements in the characteristics of the antibody and the treatment strategies used. Future trials will focus on the use of peripheral stem cell support to allow for higher administered activities and the use of combined modality strategies with radiation-enhancing chemotherapy drugs. Further efforts to reduce immunogenicity through humanization of the antibody are also planned. Finally, novel engineered, lower molecular weight, faster clearing constructs derived from cT84.66 continue to be evaluated in preclinical models as potential agents for radioimmunotherapy.

Targeting and therapy of carcinoembryonic antigen-expressing tumors in transgenic mice with an antibody-interleukin 2 fusion protein

The purpose of this study was to engineer a bivalent single-chain anticarcinoembryonic antigen (CEA) antibody and an interleukin 2 (IL-2) fusion protein derivative for selective tumor targeting of cytokines. The variable domains of a high affinity anti-CEA antibody, T84.66, were used to form a single-gene-encoded antibody [single-chain variable fragment joined to the crystallizable fragment, Fc (scFvFc)]. The fusion protein (scFvFc.IL-2) consisted of mouse IL-2-fused to the COOH-terminal end of the scFvFc. The engineered proteins were assembled as complete molecules and were similar to the intact anti-CEA monoclonal antibody (Mab) in antigen-binding properties. Based on IL-2 content of the fusion protein, its ability to support proliferation of CTLL-2 cells was identical with that of IL-2. Despite a molecular size similar to that of the intact Mab, the blood clearance of the fusion protein was markedly faster than that of the intact Mab or scFvFc. Incubation of radiolabeled scFvFc.IL-2 but not the intact or scFvFc antibodies in mouse serum was accompanied by the appearance of complexes, suggesting that the latter may contribute to the accelerated clearance of the fusion protein. Biodistribution and tumor targeting studies were carried out in CEA-transgenic mice bearing CEA-positive murine tumors as well as the antigen-negative parental tumor. The bivalent anti-CEA scFvFc had tumor localization properties similar to those of the intact Mab. Although fusion of IL-2 to the COOH-terminal end of the bivalent scFvFc altered its pharmacokinetic properties, the fusion antibody was able to target tumors specifically. Maximum uptake of the intact Mab, scFvFc, and scFvFc.IL-2 in CEA-positive tumors was 29.3 +/- 5.0, 19.5 +/- 2.1, and 6.6 +/- 0.9% injected dose/g, respectively. Maximum tumor localization ratios (CEA-positive/CEA-negative tumor) were similar for all three antibody types (4.6-6.0), demonstrating the antigen specificity of the tumor targeting. Significant antigen-specific targeting to CEA-positive normal tissues of transgenic mice was not observed. Although the tumor-targeting properties of the fusion protein were low, the growth of CEA-expressing (P = 0.01) but not antigen-irrelevant (P = 0.22) syngeneic tumor cells was inhibited after treatment of transgenic mice with the anti-CEA-IL-2 antibody. Therapy of CEA-expressing tumors was improved after i.v. administration of the fusion protein (P = 0.0001). These studies indicate that anti-CEA antibody-directed cytokine targeting may offer an effective treatment for CEA-expressing carcinomas. The availability of an immunocompetent CEA transgenic mouse model will also help to determine the immunotherapeutic properties of these fusion proteins.

High-resolution microPET imaging of carcinoembryonic antigen-positive xenografts by using a copper-64-labeled engineered antibody fragment

Rapid imaging by antitumor antibodies has been limited by the prolonged targeting kinetics and clearance of labeled whole antibodies. Genetically engineered fragments with rapid access and high retention in tumor tissue combined with rapid blood clearance are suitable for labeling with short-lived radionuclides, including positron-emitting isotopes for positron-emission tomography (PET). An engineered fragment was developed from the high-affinity anticarcinoembryonic antigen (CEA) monoclonal antibody T84.66. This single-chain variable fragment (Fv)-C(H)3, or minibody, was produced as a bivalent 80 kDa dimer. The macrocyclic chelating agent 1,4,7, 10-tetraazacyclododecane-N,N',N", N"'-tetraacetic acid (DOTA) was conjugated to the anti-CEA minibody for labeling with copper-64, a positron-emitting radionuclide (t(1/2) = 12.7 h). In vivo distribution was evaluated in athymic mice bearing paired LS174T human colon carcinoma (CEA positive) and C6 rat glioma (CEA negative) xenografts. Five hours after injection with (64)Cu-DOTA-minibody, microPET imaging showed high uptake in CEA-positive tumor (17.9% injected dose per gram +/- 3.79) compared with control tumor (6.0% injected dose per gram +/- 1.0). In addition, significant uptake was seen in liver, with low uptake in other tissues. Average target/background ratios relative to neighboring tissue were 3-4:1. Engineered antibody fragments labeled with positron-emitting isotopes such as copper-64 provide a new class of agents for PET imaging of tumors.

The chemistry of protein sequence analysis

N-terminal sequence analysis by Edman chemistry continues to play an important role in the structural analysis of proteins and peptides. Improvements in the sensitivity of the method have been achieved mainly at the level of increasing the sensitivity of the on-line analysis of PTH amino acids by RP-HPLC (reverse phase high performance chromatography). Using microbore columns (0.8-1.0 mm), it is possible to run standards at the 0.5-1.0 pmol level and to sequence samples in the 1-5 pmol range. Due to constraints in current chromatographic methods, it is unlikely that further improvements in sensitivity will be achieved by this approach alone. Although alternative Edman reagents, including fluorescent chemistries, have promised to increase the sensitivity of sequencing into the low femtomole range, none of the methods have progressed into routine usage. These reagents and chemistries are critically evaluated in this review, and the problems which have prevented their further development discussed. Instrumental constraints are also considered. It is concluded that the development of more sensitive methods requires further research into both the chemistry and the instrumentation, and that alternative separation and detection methods may also play a role.

Biodistribution and radioimmunotherapy of human breast cancer xenografts with radiometal-labeled DOTA conjugated anti-HER2/neu antibody 4D5

HER2/neu oncogene encodes a 185 kDa trans-membrane protein which is overexpressed in 20-30% of breast and ovarian cancers and portends a poor prognosis. We have studied the targeting and therapy of this oncoprotein with 4D5, a murine monoclonal antibody which recognizes a distinct epitope on the extracelluar domain of HER2/neu. We conjugated the antibody with an active ester of the macrocyclic chelating agent DOTA, radiolabeled the conjugate with either (111)In or (90)Y, and studied the antibody distribution and therapy, respectively, in athymic mice bearing xenografts of MCF7/HER2/neu, a human breast cancer cell line transfected with the HER2/neu oncogene. For the biodistribution of (111)In-labeled DOTA-4D5, a high specificity of tumor localization (30% ID/g) was seen with a tumor-to-blood ratio of greater than 2 at 48 h postinjection. Compared to a previously published study with (125)I-labeled 4D5 in beige nude mice bearing NIH3T3/HER2/neu xenografts [De Santes et al. (1992) Cancer Res. 52, 1916-1923], (111)In-labeled 4D5 antibody gave superior antibody uptake in tumor (30% ID/g vs 17% ID/g at 48h). In the therapy study, treatment of the nude mice bearing MCF7/HER2/neu xenografts with 100 microCi (3 microg) of (90)Y-labeled DOTA-4D5 caused a 3-fold reduction of tumor growth compared to untreated controls (injected with human serum albumin) in 40 days. Treatment of animals with 100 microCi of nonspecific antibody (90)Y-labeled DOTA-Leu16 (3 microg) had no tumor growth inhibition. Treatment with unlabeled DOTA-4D5 (3 microg) had a slight effect on tumor growth compared to untreated controls. When analyzed at the level of single animals, no effect was seen in seven of nine animals; however, in two of the animals, tumor growth inhibition was observed. Although a cold antibody therapeutic effect was unexpected at this dose level (3 microg), it may be possible that in some animals that 3 microg of antibody of (90)Y-labeled DOTA-4D5 augmented tumor growth reduction. To further explore the effects of cold antibody treatment alone, animals were treated with 100 or 400 microg of unlabeled 4D5 administered in two doses. These animals showed a 1.7-1.8-fold reduction in tumor growth over 28 days, a result less than that obtained with RIT only.

Evaluating changes in stable chromosomal translocation frequency in patients receiving radioimmunotherapy

PURPOSE

The lack of any consistent correlation between radioimmunotherapy (RIT) dose and observed hematologic toxicity has made it difficult to validate RIT radiation dose estimates to marrow. Stable chromosomal translocations (SCT) which result after radiation exposure may be a biologic parameter that more closely correlates with RIT radiation dose. Increases in the frequency of SCT are observed after radiation exposure and are highly correlated with absorbed radiation dose. SCT are cumulative after multiple radiation doses and conserved through an extended number of cell divisions. The purpose of this study was to evaluate whether increases in SCT frequency were detectable in peripheral lymphocytes after RIT and whether the magnitude of these increases correlated with estimated radiation dose to marrow and whole body.

METHODS AND MATERIALS

Patients entered in a Phase I dose escalation therapy trial each received 1-3 intravenous cycles of the radiolabeled anti- carcinoembryonic antigen (CEA) monoclonal antibody, 90Y-chimeric T84.66. Five mCi of 111In-chimeric T84.66 was co-administered for imaging and biodistribution purposes. Blood samples were collected immediately prior to the start of therapy and 5-6 weeks after each therapy cycle. Peripheral lymphocytes were harvested after 72 hours of phytohemagglutinin stimulation and metaphase spreads prepared. Spreads were then stained by fluorescence in situ hybridization (FISH) using commercially available chromosome paint probes to chromosomes 3 and 4. Approximately 1000 spreads were evaluated for each chromosome sample. Red marrow radiation doses were estimated using the AAPM algorithm and blood clearance curves.

RESULTS

Eighteen patients were studied, each receiving at least one cycle of therapy ranging from 5-22 mCi/m2. Three patients received 2 cycles and two patients received 3 cycles of therapy. Cumulative estimated marrow doses ranged from 9.2 to 310 cGy. Increases in SCT frequencies were observed after each cycle for both chromosomes 3 and 4 in 16 of 18 patients and in at least one chromosome for the remaining 2 patients. Cumulative increases in SCT frequencies ranged from 0.001 to 0.046 with no major differences observed between chromosomes 3 and 4. A linear correlation between cumulative marrow dose and increases in SCT frequencies was observed for chromosome 3 (R2 = 0.63) and chromosome 4 (R2 = 0.80). A linear correlation was also observed between increases in SCT frequency and whole body radiation dose or administered activity (R2 = 0.67-0.89). There was less correlation between observed decrease in wbc or platelet counts and marrow dose, whole body dose, or administered activity (R2 = 0.28-0.43).

CONCLUSIONS

Increases in SCT frequency were detectable in peripheral lymphocytes after low dose-rate RIT irradiation. A linear correlation was observed between increases in SCT and marrow dose, whole body dose, and administered activity. This correlation provides one of the strongest radiation dose-response and activity-response relationships observed with RIT. The detection of SCT may therefore have application as an in situ integrating biodosimeter after RIT. This biologic parameter should prove useful in comparing effects on marrow for different therapeutic radionuclides and in comparing effects of RIT and external beam radiation doses on a cGy per cGy basis. As a result, this should allow for a more direct comparison between different methods of irradiation and in further refinement of radioimmunotherapy dose estimates and dosimetry methodology.

Essential role of biliary glycoprotein (CD66a) in morphogenesis of the human mammary epithelial cell line MCF10F

Normal mammary epithelial cells express the cell surface protein biliary glycoprotein (BGP or CD66a) in a polarized manner, suggesting that this protein may play a role in the formation of mammary acini. In order to test this hypothesis, we interrupted the expression of BGP in the mammary epithelial line MCF10F when cultured in or on Matrigel, a source of extracellular matrix (ECM). When analyzed by immunofluorescence confocal microscopy, the BGP staining is confined to the lumenal surface and colocalizes with actin. Sequential scanning electron microscopy demonstrates that the MCF10F cells migrate to form clusters, followed by apoptotic cell death within the center, resulting in lumen formation. Transmission electron micrographs reveal the presence of tight junctions and desmosomes between the cells, microvilli along the lumenal surface, and typical apoptotic bodies within the lumen. When the MCF10F cells are transfected with the BGP antisense gene and grown in Matrigel, they exhibit reduced acini formation (12% and 20%) compared to untransfected cells (52%) or to cells transfected with vector only (62%). Acini formation is also significantly reduced when MCF10F cells grown in Matrigel are treated with anti-BGP antibody (18% at 100 microgram/ml), or recombinant soluble BGP (18% at 0.4 microM). In contrast, the BGP-negative MCF7 breast tumor cell line, which does not form acini when grown in matrigel, exhibits &gt;60% cell death with the occasional formation of acini, when transfected with the BGP sense gene and grown in Matrigel. These results support the hypothesis that BGP plays a role in the normal differentiation program of mammary epithelial cells, indicating that its expression is essential to the formation of the lumen. Furthermore, and as shown by others, the differentiation program depends on the presence of ECM. The lack of expression of BGP in the MCF7 breast cancer cell line suggests that the downregulation of BGP expression confers a growth advantage to these cells in ECM. In addition, we found that the MCF10F cells could be separated into a BGP-positive epithelial fraction (MCF10F-e), and a BGP-negative myoepithelial fraction (MCF10F-m). When the myoepithelial cell-enriched fraction is grown on Matrigel, web-like structures are formed. These cells have a typical spindle shape cell morphology and express keratin, alpha-smooth muscle actin and vimentin, markers of the myoepithelial cell phenotype. When MCF10F-m cells are treated with IFNgamma, they express CEA (carcinoembryonic antigen) but not BGP. Since breast carcinomas, especially in situ carcinomas, express CEA, this finding may suggest a heretofore unappreciated relationship between myoepithelial cells and breast cancer.

Production of carcinoembryonic antigen (CEA) N-A3 domain in Pichia pastoris by fermentation

Carcinoembryonic antigen (CEA) is a 180-kDa glycoprotein found on the surface of normal colon and malignant human adenocarcinomas. Recently, a fusion protein containing two of the seven Ig-like domains present in CEA (N and A3) has been constructed and expressed in Pichia pastoris [You, Hefta, Yazaki, Wu and Shively (1998) Anticancer Res. 18, 3193-3201]. Here, we report the generation and selection of a multi-copy clone expressing this fusion protein, the optimization of the shake-flask expression protocol and the upscaled production of CEA N-A3 using fermentation technology. P. pastoris transformants secreting the CEA N-A3 domain were generated by electrotransformation of the GS115 host strain with the pPIC9K vector containing the CEA N-A3 cDNA [You, Hefta, Yazaki, Wu and Shively (1998) Anticancer Res. 18, 3193-3201] then screened for CEA N-A3 expression and G418 resistance. The recombinant CEA N-A3 domain was detected in the culture supernatant using the monoclonal anti-CEA antibody T84.66. Optimization of methanol-induction conditions resulted in a high-methanol shake-flask expression protocol yielding significantly increased CEA N-A3 levels. Fermentation and culture conditions were optimized for 5-l working-volume fermentations and CEA N-A3 was affinity purified using Ni-IDA (imino di-acetic acid) affinity chromatography from the clarified fermentation supernatant. Peptide N-glycosidase F treatment revealed that the recombinant protein was heavily glycosylated but expressed as a single polypeptide of 28 kDa with no evidence of proteolytic degradation. Our results demonstrate that functional CEA N-A3 domain can be produced in sufficient quantities in P. pastoris for structural analysis or diagnostic applications. To our knowledge, this article represents the first report on the production of a human tumour antigen through fermentation.

Initial clinical experience evaluating Yttrium-90-chimeric T84.66 anticarcinoembryonic antigen antibody and autologous hematopoietic stem cell support in patients with carcinoembryonic antigen-producing metastatic breast cancer

cT84.66 is a human/murine IgG1 with high affinity and specificity for carcinoembryonic antigen (CEA). An earlier Phase I trial defined the maximum tolerated dose for 90Y-diethylenetriaminepentaacetic acid (DTPA)-cT84.66 at 22 mCi/m2. Dose-limiting toxicities were reversible leukopenia and thrombocytopenia. The purpose of this Phase I trial was to evaluate the feasibility and toxicities of administering higher activities of 90Y-DTPA-cT84.66 with stem cell support in patients with CEA-producing breast cancer. Patients with CEA-producing breast cancer refractory to standard therapies underwent peripheral stem cell collection followed by infusion of 111indium-DTPA-cT84.66. Those patients demonstrating tumor targeting received a single therapy dose of 90Y-DTPA-cT84.66, followed by Ca-DTPA infusion for 72 h posttherapy. Stem cells were reinfused following a divided schedule. To date, seven patients have been accrued to this trial. Each patient received an imaging dose of (111)In-cT84.66. Six patients demonstrated tumor imaging and received a single cycle of 90Y-cT84.66 at 15 mCi/m2 (three patients) and 22.5 mCi/m2 (three patients). One patient did not demonstrate tumor imaging and was not treated. At these administered activities, 90Y-cT84.66 was well tolerated. No dose-limiting toxicities have been observed. All patients demonstrated hematopoietic recovery after stem cell infusion. One patient demonstrated stable disease for 4 months; one patient had stable disease and reduction of bone pain for 3 months; and a third patient experienced >50% reduction of an ovarian metastasis, resolution of malignant pleural effusion, stable pleural metastases, and stable bone scan for 14 months. Preliminary results from this ongoing Phase I trial are promising and demonstrate the feasibility and potential for antitumor effects of stem cell supported 90Y-cT84.66 therapy in patients with CEA-producing breast cancers.

Specific binding of glucosaminylmuramyl peptides to histones

Intracellular N-acetylglucosaminylmuramyl peptide-binding proteins of murine macrophages and myelomonocytic WEHI-3 cells were characterized. SDS-PAGE and Western blotting revealed proteins with molecular masses of 18, 32 and 34 kDa retaining the ability to specifically bind glucosaminylmuramyl dipeptide. The inhibition analysis demonstrated that only biologically active muramyl peptides but not inactive analogs or fragments of glucosaminylmuramyl dipeptide could inhibit glucosaminylmuramyl dipeptide-binding to these proteins. Purification of these proteins and sequencing of peptides obtained after in-gel trypsin digestion enabled us to identify the above mentioned proteins as histones H1 and H3. These findings suggest that nuclear histones might be target molecules for muramyl peptides.

A novel gene encoding a sulfur-regulated outer membrane protein in Thiobacillus ferrooxidans

Thiobacillus ferrooxidans is a Gram-negative chemolithotrophic bacterium able to oxidize ferrous iron, elemental sulfur and inorganic sulfur compounds. The oxidation of sulfur by T. ferrooxidans resulted in an expression of some outer membrane proteins (OMPs) at a level higher than that observed during ferrous iron oxidation. Among these OMPs, a protein with a molecular mass of 54 kDa was purified and 18 amino acids of the N-terminal sequence determined. Using a 54 bp PCR generated DNA product as a probe for the protein, we isolated a 4.5 kb Pst I DNA chromosomal fragment containing the corresponding gene. Sequencing 2169 bp of this fragment revealed the open reading frame codifying for the protein, consisting of 467 amino acids and a molecular mass of 49,674 Da. The mature protein was produced by the removal of a 32 amino acid signal peptide-like sequence from the N-terminus of a 499 amino acid peptide. Although no significant homology with any known protein has been found and its physiological role remains unclear, its high expression on sulfur substrates suggests a role in sulfide mineral oxidation.

A chimeric anti-CEA antibody with heavy interchain disulfide bonds deleted: molecular characterization and biodistributions in normal and tumor bearing mice

We have deleted the interchain disulfide bonds in a chimeric anti-CEA antibody (chT84.66) by mutating two cysteines in the heavy chain to glycine residues. The resulting antibody delta SSchT84.66 was expressed in high yield in a bioreactor and purified to homogeneity in a single step on an anti-idiotypic antibody affinity column. The molecular size of the antibody was 150 kDa as judged by gel filtration, SDS gel electrophoresis under non-reducing conditions, and MALDI-TOF/MS. The 150 kDa antibody had nearly identical kinetic (Kon = 1.53 x 10(6) M-1 s-1, .koff = 1.14 x 10(-5) s-1) and affinity constants (Kaff = 1.34 x 10(11) M-1) compared to the parent murine (Kaff = 1.25 x 10(11) M-1) and chimeric (Kaff = 1.16 x 10(11) M-1) antibodies when tested on biosensor chips. When delta SSchT84.66 was conjugated to the isothiocynato derivative of DTPA, radiolabeled with 111In, and injected into either normal or nude mice bearing tumor xenografts, it gave nearly identical biodistributions to chT84.66. delta SSchT84.66 and chT84.66 antibodies gave a maximum tumor uptake of 48 and 74% ID/g, and tumor to blood ratios of 5.3 and 6.2 at 48 h, respectively. We conclude that delta SSchT84.66 irreversibly associates into H2L2 dimers after concentration, that the dimers are stable under both the in vitro and in vivo conditions used in this study, and the properties of the antibody are virtually indistinguishable from the parent chT84.66 antibody.

Dose escalation trial of indium-111-labeled anti-carcinoembryonic antigen chimeric monoclonal antibody (chimeric T84.66) in presurgical colorectal cancer patients

Chimeric T84.66 (cT84.66) is a high-affinity (1.16x10(11) M(-1)) IgG1 monoclonal antibody against carcinoembryonic antigen (CEA). The purpose of this pilot trial was to evaluate the tumor-targeting properties, biodistribution, pharmacokinetics and immunogenicity of 111In-labeled cT84.66 as a function of administered antibody protein dose.

METHODS

Patients with CEA-producing colorectal cancers with localized disease or limited metastatic disease who were scheduled to undergo definitive surgical resection were each administered a single intravenous dose of 5 mg of isothiocyanatobenzyl diethylenetriaminepentaacetic acid-cT84.66, labeled with 5 mCi of 111In. Before receiving the radiolabeled antibody, patients received unlabeled diethylenetriaminepentaacetic acid-cT84.66. The amount of unlabeled antibody was 0, 20 or 100 mg, with five patients at each level. Serial blood samples, 24-hr urine collections and nuclear images were collected until 7 days postinfusion. Human antichimeric antibody response was assessed up to 6 mo postinfusion.

RESULTS

Imaging of at least one known tumor site was performed in all 15 patients. Fifty-two lesions were analyzed, with an imaging sensitivity rate of 50.0% and a positive predictive value of 76.9%. The antibody detected tumors that were not detected by conventional means in three patients, resulting in a modification of surgical management. Interpatient variations in serum clearance rates were observed and were secondary to differences in clearance and metabolic rates of antibody and antibody:antigen complexes by the liver. Antibody uptake in primary tumors, metastatic sites and regional metastatic lymph nodes ranged from 0.4% to 134% injected dose/kg, resulting in estimated 90Y-cT84.66 radiation doses ranging from 0.3 to 193 cGy/mCi. Thirteen patients were evaluated 1-6 mo after infusion for human antichimeric antibody, and none developed a response. No major differences in tumor imaging, tumor uptake, pharmacokinetics or organ biodistribution were observed with increasing protein doses, although a trend toward increasing blood uptake and decreasing liver uptake was observed with increasing protein dose.

CONCLUSION

Chimeric T84.66 demonstrated tumor targeting comparable to other radiolabeled intact anti-CEA monoclonal antibodies. Its immunogenicity after single administration was lower than murine monoclonal antibodies. These properties make 111In-cT84.66, or a lower molecular weight derivative, attractive for further evaluation as an imaging agent. Yttrium-90 dosimetry estimates predict potentially cytotoxic radiation doses to select tumor sites, which makes 90Y-cT84.66 also appropriate for further evaluation in Phase I radioimmunotherapy trials. Although clinically important changes in biodistribution, pharmacokinetics and tumor targeting with increasing protein doses of 111In-cT84.66 were not demonstrated, the results do suggest that antibody clearance from the blood is driven by hepatic uptake and metabolism, with more rapid blood clearance seen in patients with liver metastases. These patients with rapid clearance and potentially unfavorable biodistribution for imaging and therapy may, therefore, be a more appropriate subset in which to evaluate the role of administering higher protein doses. This underscores the need to further identify, characterize and understand those factors that influence the biodistribution and clearance of radiolabeled anti-CEA antibodies, to allow for better selection of patients for therapy and rational planning of radioimmunotherapy.

Solid-phase synthesis and characterization of carcinoembryonic antigen (CEA) domains

Carcinoembryonic antigen (CEA), a 180,000 dalton cell surface glycoprotein expressed on tumors of the colon, breast, ovary, and lung, has seven predicted immunoglobulin-like domains (N-A1-B1-A2-B2-A3-B3), most of which are recognized by distinct monoclonal antibodies. To study the individual domains, we have prepared several of the domains (N, A3, B3, and A3-B3) by solid-phase peptide synthesis. The syntheses were performed by the Fmoc method using single couplings, elevated temperatures for both the coupling and deblocking reactions, and a flexible solvent system for the coupling reactions. The syntheses were accomplished on an in-house built synthesizer which allowed for temperature control and flexible solvent control during the course of the coupling reactions. Due to the large size of the peptides (84-184 residues), it was anticipated that the overall purity of the final product would not exceed 60% even for an average coupling yield of 99.5%. Therefore, several of the peptides were synthesized with a His6 "tail" at the amino terminus, allowing for purification on a Ni-NTA chelate column. For the most part, the purified peptides exhibited single sharp peaks by RP-HPLC, migrated at their expected molecular weights by gel permeation chromatography, gave correct masses by electrospray ionization or matrix-assisted laser desorption ionization time of flight mass spectrometry, gave the expected amino acid analyses, N-terminal sequences, and tryptic maps, and bound their appropriate monoclonal antibodies. The N-domain was extremely hydrophobic, requiring 6M guanidinium hydrochloride for solubilization, the A3 domain was soluble in dilute acid, and the B3 domain had an intermediate solubility. The affinity constants of the A3 domain and several mutants (also made by peptide synthesis) are reported, along with characterization of the 178 amino acid two-domain peptide, A3-B3. Although there is no evidence for proper folding of these domains by NMR, their ability to bind monoclonal antibodies with high affinity suggests that this is a plausible approach for producing individual domains of CEA.

Preparation and in vitro characterization of gentamycin-impregnated biodegradable beads suitable for treatment of osteomyelitis

A new method for preparing poly(L-lactide) (PLA) biodegradable beads impregnated with an ionic aminoglycoside, gentamycin, is described. The process employs hydrophobic ion pairing to solubilize gentamycin in a solvent compatible with PLA, followed by precipitation with a compressed antisolvent (supercritical carbon dioxide). The resulting precipitate is a homogeneous dispersion of the ion-paired drug in PLA microspheres. The microspheres are approximately 1 microm in diameter and can be compressed into beads (3-6 mm in diameter) strung on surgical sutures for implantation. The bead strings exhibit no significant change in release kinetics upon sterilization with a hydrogen peroxide plasma (Ster-Rad). The kinetics of gentamycin release from the PLA beads are consistent with a matrix-controlled diffusion mechanism. While nonbiodegradable poly(methyl methacrylate) (PMMA) beads initially release gentamycin in a similar manner, the drug release from PMMA ceases after 8 or 9 weeks, while the PLA beads continue to release drug for over 4 months. Moreover, only 10% of the gentamycin is released from the PMMA beads, while PLA beads release more than 60% of their load, if serum is present in the release medium. The PLA system displays improved release kinetics relative to PMMA, is biodegradable, is unaltered by gas sterilization, can be used for a range of antibiotics, and can be manipulated without disintegration. These are all desirable properties for an implantable drug delivery system for the prevention or treatment of osteomyelitis.

Expression, purification, and characterization of a two domain carcinoembryonic antigen minigene (N-A3) in pichia pastoris. The essential role of the N-domain

Carcinoembryonic antigen (CEA) is a 180 kDa glycoprotein expressed on the surface of normal and malignant human colon. The structure of CEA has seven predicted Ig-like domains (N-A1-B1-A2-B2-A3-B3) that are encoded by separate exons and contain independent epitopes that are recognized by monoclonal antibodies. The N-domain mediates homotypic cell adhesion as shown by deletion expression analysis, and may also interact with the A3 domain. Although we have been unsuccessful in expressing these domains in high yields of active protein in either bacterial or mammalian expression systems, we now report high yield expression in Pichia pastoris of a mini-gene (N-A3) comprising the N and A3 domains of CEA, and containing epitopes for the monoclonal antibodies T84.1 and T84.66. N-A3 was constructed by splice overlap PCR from the CEA gene and fused to the yeast alpha-mating factor leader sequence and an N-terminal His6 tag. The secreted protein gave high level expression (20 micrograms/mL) and was purified in two steps using Ni(NTA) affinity chromatography followed by reversed phase HPLC. The purified protein (yield 6 mg from 600 mL of supernatant) had a single N-terminal sequence, the expected amino acid composition, and retained full reactivity to both T84.1 and T84.66 compared to native CEA. BIAcore analysis gave a Kaff of 4.4 x 10(10) M-1 for the binding of N-A3 to T84.1 and 2.2 x 10(10) M-1 for the binding of N-A3 to T84.66. The molecular weight of N-A3 was 37 kDa before and 24 kDa after enzymatic deglycosylation as determined by SDS gel electrophoresis. The average N-glycosyl unit was calculated at 1850 Da (for 7 N-linked sites) suggesting a GN2Man9 oligosaccharide structure. N-A3 migrated as a dimer at 80 kDa and a monomer at 40 kDa on gel filtration analysis performed at pH 7.5, and 4.0, respectively. CEA exhibited the same conversion of dimers to monomers when analyzed by gel filtration at neutral and acid pH. The availability of this highly active CEA mini-gene should enable further structure-function studies including epitope analysis and investigation of monomer-dimer interactions.

Expression of biliary glycoprotein (CD66a) in normal and malignant breast epithelial cells

Biliary glycoprotein (BGP, CD66a, or C-CAM-1) is a cell adhesion glycoprotein expressed in colon, liver, and hematopoietic tissues. Four major isoforms (a-d) of BGP are expressed in most epithelial tissues by alternative mRNA splicing from a single gene. Since BGP is down regulated in colon cancer and in premalignant colonic adenomas, it has been of interest to study its expression in other tumors. Using immunohistochemistry with a BGP specific antibody, and mRNA analysis by in situ hybridization, RNase protection, and RT-PCR, we show here that BGP is expressed to the same extent in both normal and malignant breast, demonstrating that BGP is not down regulated in breast cancer. In normal breast, BGP expression is confined to the apical surface of ductal and lobular epithelial cells, while in invasive carcinoma of the breast, BGP is expressed throughout the cytoplasm. In situ hybridization shows a specific pattern of BGP expression in both normal and malignant breast epithelium. RNase protection analysis confirms the immunohistochemistry results and shows no quantitative differences between normal and malignant breast. RT-PCR analysis agrees with these results and shows that only 3 of the 4 major isoforms (a, c, d) of BGP are expressed in normal and malignant breast. Since recent studies by Turbide et al (Cancer Res 57: 2781-2788, 1997) have shown that the ratio of murine BGP isoforms may affect tumor suppression in colonic cancer, it is proposed here that the isoform difference between human breast and colon may account for the observed lack of BGP down-regulation in breast vs colon cancer.

Kinetic and affinity constants of epitope specific anti-carcinoembryonic antigen (CEA) monoclonal antibodies for CEA and engineered CEA domain constructs

BACKGROUND

Carcinoembryonic antigen (CEA) is a human tumor antigen with the domain structure N-A1-B1-A2-B2-A3-B3, in which each domain is predicted to have an Ig-like fold and is known to bind epitope specific anti-CEA antibodies.

OBJECTIVE

To determine the affinity constants of several domain specific anti-CEA antibodies using purified recombinant or synthetic domains.

RESULTS AND CONCLUSION

We have determined the kinetic and affinity constants of several anti-CEA antibodies for CEA, CEA domains (A3-B3) expressed in HeLa cells, and a synthetic peptide corresponding to the A3 domain using a BIAcore biosensor. There was no difference in affinity for CEA among a murine (mT84.66), a mouse/human chimeric form (cT84.66) or a disulfide deleted version (delta SScT84.66) of this antibody. There was less than a five-fold drop in affinity of murine T84.66 for the A3-B3 domain expressed in HeLa cells compared to CEA. The synthetic A3 domain had an affinity constant for mT84.66 which was ten-fold less than for CEA. The affinity constants for CEA with several other anti-CEA monoclonal antibodies, including three antibodies which have almost identical CDR sequences (CEA.281, CEA.11 and CEM231) were also determined. CEM231 which had a two-fold higher affinity constant for CEA than either CEA.281 or CEA.11 had a two-fold faster on-rate which accounts for its higher affinity constant. This difference may be due to one or more of the amino acid differences present in H1 (N vs. S or D) and H3 (A vs. V).

Shared tumor antigens in colorectal carcinoma and neuroendocrine tumors

ND4 monoclonal antibody recognizes a tumor marker found on poorly differentiated colorectal cancer. We demonstrate its expression in 25% of gastrointestinal neuroendocrine tumors, which also express CEA in 37% of cases. As in colorectal cancer the ND4 marker is predominantly membrane bound in a colonic neuroendocrine tumor cell line, LCC-18 (p < 0.05). The ND4 marker is absent in a poorly differentiated colorectal cancer cell line that does not express CEA or other tumor antigens. Shed antigen in the serum of patients with neuroendocrine tumors is detected in only five of seven patients with the carcinoid syndrome and two of four of those without evidence of the syndrome. However, the reactivity was less in the patients with localized disease, and this test is unlikely to be of diagnostic utility in this group of patients. The sharing of this antigen in colorectal cancer and neuroendocrine tumors is not universal, but does support the common-cell progenitor theory for the origin of these tumors.

Maleimidocysteineamido-DOTA derivatives: new reagents for radiometal chelate conjugation to antibody sulfhydryl groups undergo pH-dependent cleavage reactions

We have synthesized two bifunctional derivatives of the macrocyclic chelating agent 1,4,7,10-tetraazacyclododecane-N,N',N",N"-tetraacetic acid (DOTA) equipped with maleimide groups for conjugation to reduced disulfide bonds of monoclonal antibodies. Using water-soluble carbodiimide chemistry, DOTA was coupled to L-cysteine to incorporate both a "pendant-type" carboxyl group for metal coordination and an orthogonal thiol group for protein attachment. The homobifunctional reagent 1,6-bis(maleimido)hexane was then used to introduce the maleimide functionality via a sulfide linkage to the macrocycle, and alternatively, the sulfide group was converted to a sulfone side chain. Both maleimide derivatives were conjugated to the anticarcinoembryonic antigen chimeric monoclonal antibody cT84.66 after light reduction of the mAb with dithiothreitol. In this manner, antibody conjugates were prepared which afforded near-quantitative labeling with the radiometals 111In(III) and 90Y(III) as well as quantitative immunoreactivity. Radioimmunoconjugates prepared with the sulfide and sulfone compounds exhibited relatively rapid linker-dependent radiometal loss when incubated in human serum and aqueous solutions at physiological temperature and pH. The unconjugated maleimidocysteineamido-DOTA derivatives and their Y(III) complexes were incubated in aqueous solution at 37 degrees C, and the resulting decomposition products were analyzed by HPLC and mass spectrometry. These studies revealed that the two bifunctional chelating agents underwent linker-specific cleavage reactions which were considerably faster at pH 7.4 than at pH 5.4. The chemically labile linker systems are expected to release chelated radiometal from mAb conjugates in a pH-dependent manner. This property may impart favorable tumor uptake and normal tissue clearance on radioimmunoconjugates prepared with these reagents, on the basis of the observation that many solid tumors are significantly more acidic than normal tissues.

Biodistribution of 111In- and 90Y-labeled DOTA and maleimidocysteineamido-DOTA conjugated to chimeric anticarcinoembryonic antigen antibody in xenograft-bearing nude mice: comparison of stable and chemically labile linker systems

Biodistributions of two radiometal chelate conjugates of the human/murine chimeric anticarcinoembryonic antigen monoclonal antibody cT84.66 were obtained in nude mice bearing LS174T human colorectal carcinoma xenografts. Derivatives of the macrocyclic chelating agent 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA) were covalently attached to the antibody by a stable amide linkage and by a maleimidocysteineamido side chain (MC-DOTA) that has been shown to be chemically labile at physiological temperature and pH. Biodistributions of both 111In and 90Y labels were obtained in these studies. At common biodistribution time points, it was found that the 111In label had greater uptake in the liver than 90Y for both conjugates. No significant differences were found with respect to bone uptake of 90Y using either chelate. Blood curves were generally lower at comparable time points for MC-DOTA, indicative of faster clearance as compared to DOTA. Tumor uptake was high for both conjugates (57-68% ID/g at 48 h), with a longer tumor residence time in the case of the DOTA conjugate, probably a result of its longer blood circulation times. We conclude that bone uptake of 90Y would be minimal if either DOTA or MC-DOTA were used as the bifunctional chelator. This would imply preference for these macrocyclic ligands if radiation doses to the bone marrow would be considered to be dominated by skeletal uptakes. Alternatively, if bone marrow radiation dose is dominated by circulating antibody, the chemically labile linker system employed by the MC-DOTA conjugate offers the advantage of enhanced blood clearance.

The 95-kilodalton membrane glycoprotein overexpressed in novel multidrug-resistant breast cancer cells is NCA, the nonspecific cross-reacting antigen of carcinoembryonic antigen

Human breast carcinoma MCF-7/AdrVp cells display a novel multidrug resistance phenotype that is characterized by the overexpression of a 95-kDa membrane glycoprotein (p95) and by marked reduction in intracellular anthracycline accumulation, without overexpression of P-glycoprotein or the multidrug resistance protein MRP. p95 is also highly expressed in multidrug-resistant NCI-H1688 cells derived from a human small cell lung carcinoma. Deglycoslyated p95 from NCI-H1688 cells was isolated by two-dimensional gel electrophoresis and then digested with trypsin. The tryptic peptides were analyzed by mass spectrometry and microsequencing. These analyses identified p95 to be identical to NCA-90, the nonspecific cross-reacting antigen related to the carcinoembryonic antigen (CEA). Further confirmation that p95 is indeed NCA-90 was obtained by Northern and Western blot studies using probes or antibodies specific for p95, NCA-90, or CEA family members. Western blot studies also revealed that CEA itself is overexpressed in MCF-7/AdrVp cells compared to parental MCF-7/W cells. The enforced expression of NCA-90 protein in HeLa cells stably transfected with NCA-90 cDNA did not result in increased resistance of the transfected cells to daunorubicin or a decrease in daunorubicin accumulation in the transfected cells compared to cells transfected only with the expression vector. However, a recent report by H. Kawaharata et al. (Int. J. Cancer, 72: 377-382, 1997) of diminished accumulation, retention, and cytotoxicity of doxorubicin in EJNIH3T3 cells in which enforced expression of CEA was accomplished leaves open the possibility that the overexpression of CEA, possibly in combination with that of NCA-90, could account at least in part for the drug resistant phenotype displayed by MCF-7/AdrVp cells.

Clinical evaluation of indium-111-labeled chimeric anti-CEA monoclonal antibody

Chimeric T84.66 (cT84.66) is a high-affinity (1.16 x 10[11] M[-1]) IgG1 monoclonal antibody (MAb) against carcinoembryonic antigen (CEA). This pilot trial evaluated the tumor-targeting properties, biodistribution, pharmacokinetics and immunogenicity of 111In-labeled cT84.66.

METHODS

Patients with CEA-producing metastatic malignancies were administered a single intravenous dose of 5 mCi 111In-diethylenetriaminepentaacetic acid-cT84.66. Serial blood samples, 24-hr urine collections and nuclear images were collected up to 7 days postinfusion. Human antichimeric antibody response was assessed up to 6 mo postinfusion.

RESULTS

Imaging of at least one known tumor site was observed in 14 of 15 (93%) patients. Seventy-four lesions were analyzed with an imaging sensitivity rate of 45.1% and a positive predictive value of 94.1%. In one patient, two additional bone metastases developed within 6 mo of antibody administration at sites initially felt to be falsely positive on scan. One patient developed a human antichimeric antibody response predominantly to the murine portion of the antibody. The antibody cleared serum with a median T(1/2alpha) of 6.53 hr and a T(1/2beta) of 90.87 hr. Interpatient variations in serum clearance rates were observed and were secondary to differences in clearance and metabolic rates of antibody-antigen complexes by the liver. One patient demonstrated very rapid clearance of antibody by the liver, which compromised antibody localization to the primary tumor. Antibody uptake in primary and metastatic tumors ranged from 0.5% to 10.5% injected dose/kg, resulting in estimated radiation doses ranging from 0.97 to 21.3 cGy/mCi 90Y. Antibody uptake in regional lymph nodes ranged from 1.3% to 377% injected dose/kg, resulting in estimated radiation doses ranging from 2.0 to 617 cGy/mCi 90Y.

CONCLUSION

Chimeric T84.66 demonstrated tumor targeting that was comparable to that of other radiolabeled intact anti-CEA Mabs. Its immunogenicity after single administration was lower than murine Mabs. These properties make cT84.66 or a lower molecular weight derivative attractive for further evaluation as an imaging agent. These same properties also make it appropriate for future evaluation in Phase I therapy trials. Finally, a wide variation in the rate of antibody clearance was observed, with one patient demonstrating very slow clearance, resulting in the highest estimated marrow dose of the group, and one patient demonstrating unusually rapid clearance, resulting in poor antibody localization to tumor. Data from this study suggest that serum CEA levels, antibody-antigen complex clearance and, therefore, antibody clearance are influenced by both the production and clearance rates of CEA. This underscores the need to further identify, characterize and understand those factors that influence the biodistribution and clearance of radiolabeled anti-CEA antibodies to allow for better selection of patients for therapy and rational planning of radioimmunotherapy.

Persistent efficacy of doramectin against experimental challenge with Ostertagia ostertagi in cattle

Two studies were conducted in North America to evaluate the persistent efficacy of doramectin injectable solution against experimental challenge with infective larvae of Ostertagia ostertagi. In both studies, four groups of 10 randomly-assigned calves, negative for trichostrongyle-type eggs on fecal examination, were treated subcutaneously in the midline of the neck with saline (1 ml 50 kg-1) on Day 0 or doramectin (200 micrograms kg-1 = 1 ml 50 kg-1) on Day 0, 7, or 14. Two additional calves from the same pool of animals were randomly assigned as larval-viability monitors and received no treatment. Beginning on Day 14 and continuing through Day 28, the 40 treated calves each were given approximately 1000 infective larvae of O. ostertagi by gavage daily; the two larval-viability monitors were inoculated in a similar manner with approximately 30,000 larvae as a single dose on Day 28. Animals were slaughtered on Day 42 in one study and on Days 42, 43, or 46 in the second. The abomasum from each calf was harvested and processed for worm recovery. A 2% aliquot of abomasal contents plus wash was examined for worm quantification and identification. Geometric mean O. ostertagi burdens were calculated from the log (O. ostertagi count + 1) and were used to estimate percentage reduction. In both studies, doramectin injectable solution was > or = 99.6% efficacious in reducing infection resulting from challenge with infective larvae of O. ostertagi for at least 21 days posttreatment; by 28 days posttreatment, efficacy was 87.3% in one study and 99.7% in the other.

Human carcinoembryonic antigen and biliary glycoprotein can serve as mouse hepatitis virus receptors

Receptors for murine coronavirus mouse hepatitis virus (MHV) are members of the murine carcinoembryonic antigen (CEA) gene family. Since MHV can also infect primates and cause central nervous system lesions (G. F. Cabirac et al., Microb. Pathog. 16:349-357, 1994; R. S. Murray et al., Virology 188:274-284, 1992), we examined whether human CEA-related molecules can be used by MHV as potential receptors. Transfection of plasmids expressing human carcinoembryonic antigen (hCEA) and human biliary glycoprotein into COS-7 cells, which lack a functional MHV receptor, conferred susceptibility to two MHV strains, A59 and MHV-2. Domain exchange experiments between human and murine CEA-related molecules identified the immunoglobulin-like loop I of hCEA as the region conferring the virus-binding specificity. This finding expands the potential MHV receptors to primate species.

Neuropeptide Y 3-36 is an endogenous ligand selective for Y2 receptors

Neuropeptide Y (NPY 1-36) binds to Y1 and Y2 receptors with similar affinity. No endogenous molecular form of NPY with selectivity for Y1 or Y2 receptors has been described so far. We report the presence of an endogenous fragment of NPY in porcine brain, NPY 3-36, which lacks the amino-terminal dipeptide Tyr-Pro of NPY 1-36. NPY 3-36 accounts for 35% of NPY-like immunoreactivity in porcine brain. We have compared binding of NPY 3-36 and NPY 1-36 in model systems of Y1-like (SK-N-MC cells) and Y2-like receptors (CHP234 cells). NPY 3-36 and NPY 1-36 had similarly high affinity for Y2-like receptors on CHP234 cells, but NPY 3-36 had a 1000-fold lower affinity than NPY 1-36 for Y1-like receptors on SK-N-MC cells. Thus amino-terminal cleavage of NPY 1-36 generating NPY 3-36 converts an unselective Y1/Y2 receptor ligand into a highly Y2 selective ligand. This may be a means of fine tuning NPY biological actions.

Role of interferon regulatory factor-1 in the induction of biliary glycoprotein (cell CAM-1) by interferon-gamma

Biliary glycoprotein (BGP), also known as C-CAM-1, has been shown to be down-regulated in colon and prostate tumors. Previously, we demonstrated that BGP mRNA is up-regulated by interferon-gamma (IFN-gamma) in colon cancer cell lines (Takahashi, H., Okai, Y., Paxton, R. J., Hefta, L. J. F., and Shively, J. E. (1993) Cancer Res. 53, 1612-1619). We now show that the BGP promoter contains an interferon-sensitive response element (ISRE) that is specifically protected in in vivo footprints. Interferon regulatory factor-1 (IRF-1) was identified as the ISRE-binding factor by electrophoretic mobility shift assays. The induction of IRF-1 mRNA by IFN-gamma in HT-29 cells reaches a maximum at 6 h and is superinduced by cycloheximide. Four mRNA species for BGP are induced by IFN-gamma, the major band of which is inhibited by cycloheximide. Transfection of HT-29 cells with an IRF-1 expression plasmid (pAct-1) transactivates a BGP promoter reporter gene containing wild-type (but not mutant) ISRE. Electrophoretic mobility shift assay analysis of a second footprint reveals the binding of Sp1, an Sp1-like protein, and upstream stimulatory factor. The Sp1-like complex was also induced by IFN-gamma treatment of HT-29 cells and may be a second point of transcriptional control for the BGP gene.

Minibody: A novel engineered anti-carcinoembryonic antigen antibody fragment (single-chain Fv-CH3) which exhibits rapid, high-level targeting of xenografts

A novel engineered antibody fragment (VL-VH-CH3, or "minibody") with bivalent binding to carcinoembryonic antigen (CEA) was produced by genetic fusion of a T84.66 (anti-CEA) single-chain antibody (scFv) to the human IgG1 CH3 domain. Two designs for the connecting peptide were evaluated. In the T84.66/212 LD minibody, a two-amino acid linker (generated by fusion of restriction sites) was used to join VH and CH3. In the T84.66/212 Flex minibody, the human IgG1 hinge plus an additional 10 residues were used as the connecting peptide. Size exclusion chromatography of purified minibodies demonstrated that both proteins had assembled into Mr80,000 dimers as expected. Furthermore, analysis by SDS-PAGE under nonreducing conditions was consistent with disulfide bond formation in the hinge of the T84.66 Flex minibody. Purified minibodies retained high affinity for CEA (KA, 2 x 10(9) M(-1)) and demonstrated bivalent binding to antigen. Tumor targeting properties were evaluated in vivo using athymic mice bearing LS174T human colon carcinoma xenografts. 123I-labeled T84.66 minibodies demonstrated rapid, high tumor uptake, reaching 17% injected dose/gram (%ID/g) for the LD minibody and 33%ID/g for the Flex minibody at 6 h following injection. Radioiodinated minibody also cleared rapidly from the circulation, yielding high tumor:blood uptake ratios: 44.5 at 24 h for the LD minibody and 64.9 at 48 h for the Flex minibody. Rapid localization by the T84.66/212 Flex minibody allowed imaging of xenografts at 4 and 19 h after administration.

Evidence that CCK-58 has structure that influences its biological activity

Many biologically active peptides exist in multiple molecular forms, but the functional significance of regions outside the region of bioactivity is unknown. The biological and immunological data presented in this study indicate that cholecystokinin-58 (CCK-58), unlike other forms of cholecystokinin, has structure that influences its bioactivity. CCK-58 was purified from acid extracts of canine intestinal mucosa until a single absorbance peak was obtained during reverse-phase chromatography. Amino acid analysis precisely determined the peptide concentrations of purified CCK-58 and synthetic CCK-8. Our hypothesis was that if the amino terminus of CCK-58 influences its bioactivity then its activity would be modified when this region was removed from the peptide. To evaluate the importance of the amino terminus of CCK-58 to influence its biological activity, the abilities of CCK-58 and CCK-8 to release amylase from pancreatic acini were compared before and after tryptic digestion. Tryptic digestion of CCK-58 decreased the half-maximal stimulation (EC50) for amylase release from 96 to 28 pM. The EC50 for digested CCK-58 was similar to that for CCK-8 (17 pM). These results suggest that CCK-58 has a structure that shields its bioactive carboxyl terminus. This is further supported by the finding that carboxyl fragments generated from CCK-58 by trypsin or by partial acid hydrolysis were greater than twofold more immunoreactive than the intact CCK-58. The diminished activity of CCK-58 SK shields the carboxyl terminus, which is important to its biological and immunological activities.